Mobile devices are continuing to increase in popularity and the processing capability continues to increase. Accordingly, more and more tasks are performed on mobile devices. In order to ensure the continued proliferation of mobile devices extending the life of the batteries used to power the mobile devices is a necessity. High current peaks (wide current fluctuations) for the mobile device significantly increases the power loss of the mobile device.
The significant power loss (P) is due to a squared relationship with current (I), where the power loss equals the product of the current squared and the resistance (R), such that P=I2R. Both the internal resistance (cell impedance) of the battery and the resistance of the power delivery path from the battery to the mother board (e.g., circuits, connectors, circuit board) effect the power loss of the device. By way of example, Lithium (Li)-ion battery cells may have a cell impedance of approximately 70-350 mili-ohms (mΩ) and older batteries with many charge/discharge cycles have even higher cell impedance. The power delivery path may have a resistance of about 30 mΩ. The power loss reduces the actual amount of usable energy from the battery for the mobile device (actual energy from the battery is less than the specified battery capacity).
FIG. 1 illustrates an example graph of the relationship between system power consumption and power loss. The power loss is associated with a battery powering the system and the power delivery path. The relationship is not linear due to the squared relationship between power loss and current. As illustrated, when the system power increases three fold from 5 watts (W) to 15 W the power loss increases ten fold from 0.3 W to 3 W.
High current peaks may also temporarily cause deeper battery voltage drops, and if the temporary voltage drops go below a defined cut-off voltage, the system may shut-down prematurely. Furthermore, the trend for some processors is to enter an idle state quicker to reduce power consumption. This trend may decrease platform power but may increase the peak currents further which will result in an increased power loss and reduction in the actual amount of usable energy from the battery.